The Bentley 6½ Litre and the high-performance Bentley Speed Six were

rolling chassis A rolling chassis is the fully-assembled chassis of a motor vehicle (car, truck, bus, or other vehicle) without its coachwork, bodywork. It is equipped with running gear (engine and drivetrain) and ready for delivery to a coachbuilder to be compl ...

produced by

Bentley Bentley Motors Limited is a British designer, manufacturer and marketer of Luxury vehicle, luxury cars and Sport utility vehicle, SUVs. Headquartered in Crewe, England, the company was founded by W. O. Bentley (1888–1971) in 1919 in Crickle ...

from 1926 to 1930. The Speed Six, introduced in 1928, became the most successful racing Bentley. Two Bentley Speed Sixes became known as the ''Blue Train Bentleys'' after their owner Woolf Barnato raced the Blue Train in 1930.

Background

By 1924 Bentley had been in business for five years. He decided to build a larger chassis than the 3 Litre, with a smoother, more powerful, engine. The new chassis would be more suitable for the large and heavy limousine bodies that many of his customers were then putting on his

sports car A sports car is a type of automobile that is designed with an emphasis on dynamic performance, such as Automobile handling, handling, acceleration, top speed, the thrill of driving, and Auto racing, racing capability. Sports cars originated in ...

chassis. The resulting car would be more refined and better suited for comfortable general motoring.

Prototype race

Bentley built a

development mule A development mule, also known as test mule or simply mule, in the automotive industry is a testbed vehicle equipped with prototype components requiring evaluation. They are often camouflaged to cover their designs. Application Mules are nec ...

with a 4¼-litre

straight-six engine A straight-six engine (also referred to as an inline-six engine; abbreviated I6 or L6) is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine balanc ...

derived from the 3 Litre's

four-cylinder The engine configuration describes the fundamental operating principles by which internal combustion engines are categorized. Piston engines are often categorized by their cylinder layout, valves and camshafts. Wankel engines are often categoriz ...

engine. To disguise the car's origin, it had a large, wedge-shaped radiator and was registered as a "Sun". The chassis was given a large very lightweight Weymann-type tourer body built by Freestone and Webb. W. O. Bentley combined one of his road tests of the "Sun" with a trip to see the 1924 French Grand Prix in

Lyon Lyon (Franco-Provençal: ''Liyon'') is a city in France. It is located at the confluence of the rivers Rhône and Saône, to the northwest of the French Alps, southeast of Paris, north of Marseille, southwest of Geneva, Switzerland, north ...

. On his return trip to the ferry at

Dieppe Dieppe (; ; or Old Norse ) is a coastal commune in the Seine-Maritime department, Normandy, northern France. Dieppe is a seaport on the English Channel at the mouth of the river Arques. A regular ferry service runs to Newhaven in England ...

, W. O. encountered another disguised car at a three-way junction. W. O. and the

Rolls-Royce Rolls-Royce (always hyphenated) may refer to: * Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct Automobiles * Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...

test driver recognized each other and began racing each other along the '' routes nationales''. This street race continued until the Rolls-Royce driver's hat blew off and he had to stop to retrieve it. The Sun's tyres were heavily worn when W.O. got to the ferry at Dieppe.

6½ Litre

Realizing from the impromptu race that the Sun had no performance advantage over Rolls-Royce's latest development, W. O. increased the bore of his six-cylinder engine from to . With a

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

, the engine had a displacement of 6.6 L () Like the four-cylinder engine, Bentley's six included an overhead

camshaft A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition syst ...

, 4 valves per cylinder, and a single-piece engine block and cylinder head cast in iron, which eliminated the need for a head gasket. In base form, with a single Smiths 5-jet carburettor, twin

ignition magneto An ignition magneto (also called a high-tension magneto) is an older type of ignition system used in spark-ignition engines (such as petrol engines). It uses a magneto and a transformer to make pulses of high voltage for the spark plugs. The old ...

s, and a compression ratio of 4.4:1, the Bentley 6½ Litre delivered at 3500 RPM. Although based on the 3 Litre's engine, the 6½ engine incorporated many improvements. The 3 Litre's cone-type

clutch A clutch is a mechanical device that allows an output shaft to be disconnected from a rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does th ...

was replaced by a dry-plate design that incorporated a clutch brake for fast gear changes, and the car had power-assisted four-wheel brakes with finned

drums The drum is a member of the percussion instrument, percussion group of musical instruments. In the Hornbostel–Sachs classification system, it is a membranophones, membranophone. Drums consist of at least one Acoustic membrane, membrane, c ...

. The front brakes had 4 leading shoes per drum. By operating a patented compensating device, the driver could adjust all four brakes to correct for wear while the car was moving, which was particularly advantageous during races. A variety of

wheelbase In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...

s were provided ranging from ; the most popular was 150 inches.

Speed Six

The Bentley Speed Six chassis was introduced in 1928 as a more sporting version of the Bentley 6½ Litre. With a single-port block, two SU carburettors, a high-performance camshaft, and a compression ratio of 5.3:1, the Speed Six's engine produced at 3500 rpm. The Speed Six chassis was available to customers with wheelbases of , , and . The 138 inch wheelbase was the most popular. The

Criminal Investigation Department The Criminal Investigation Department (CID) is the branch of a police force to which most plainclothes criminal investigation, detectives belong in the United Kingdom and many Commonwealth of Nations, Commonwealth nations. A force's CID is disti ...

of the

Western Australia Police The Western Australia Police Force, colloquially WAPOL, provides police services throughout the state of Western Australia to a population of 2.66 million people, of which 2.11 million reside in the Perth Metropolitan Region. Western Australia h ...

operated two saloon-bodied examples as patrol cars. In March 1930, Barnato raced against the Blue Train in a Speed Six with H. J. Mulliner saloon coachwork, reaching his club in London before the train was due in the station at Calais. It had generally been believed that the car in the race was a Gurney Nutting Sportsman Coupé, but that car was delivered to Barnato in May 1930, more than a month after the race.

Factory racing cars

The racing version of the Speed Six had a wheelbase of and an engine with a compression ratio of 6.1:1 that produced at 3500 rpm. Successful in racing, these cars won the

24 Hours of Le Mans The 24 Hours of Le Mans () is an endurance-focused Sports car racing, sports car race held annually near the city of Le Mans, France. It is widely considered to be one of the world's most prestigious races, and is one of the races—along with ...

in 1929 and 1930 with Bentley Boys drivers "Tim" Birkin, Glen Kidston, and Woolf Barnato, the chairman of Bentley Motors.

Production

* 6½ Litre: 362 * Speed Six: 182

Gallery

File:Blue Train Bentley 6½-litre saloon.jpg, Woolf Barnato's Speed Six H. J. Mulliner saloon, in which he raced against the Blue Train File:1930 Bentley Speed Six Nutting Coupe (3828597253).jpg, 1930 Gurney Nutting Sportsman Coupé, often believed to be the car that raced the Blue Train; in fact delivered to Barnato weeks after the race. Photo from 2009 Concours. File:1930 Bentley Speed Six Nutting Coupe (3828596647).jpg, Side view File:1928 Bentley 6½ Litre Tourer KD2111, VandenPlas lhs.jpg, Bentley 6½ Litre Tourer File:1929 Bentley "Speed Six" IMG 9625 - Flickr - nemor2.jpg, Bentley Speed Six drophead coupé File:Bentley Speed Six.JPG, Bentley Speed Six prepared for racing File:Bentley 6,5-Litre Tourer.jpg, Bentley 6½-Litre Tourer File:Bentley 6,5-Litre Speed Six Tourer 1930.jpg, Bentley 6½-Litre Speed Six Tourer 1930 File:1930 Bentley Speed Six - Old Number 2 int 4668554133.jpg, Bentley Speed Six interior

Notes

References

;Print * * * * * * ;Online * * * {{Bentley Cricklewood timeline 1921 to 1931 6 Cars introduced in 1926 1930s cars 24 Hours of Le Mans race cars Le Mans winning cars Cars discontinued in 1930